부산대학교 도서관

Background cosmological dynamics for a universe with matter, a scalar field non-minimally derivative coupling to Einstein tensor under power-law potential and holographic vacuum energy is considered here. The holographic IR cutoff scale is apparent horizon which, for accelerating universe, forms a trapped null surface in the same spirit as blackhole's event horizon. For non-flat case, effective gravitational constant can not be expressed in the Friedmann equation. Therefore holographic vacuum density is defined with standard gravitational constant in stead of the effective one. Dynamical and stability analysis shows four independent fixed points. One fixed point is stable and it corresponds to $w_{\text{eff}} = -1$. One branch of the stable fixed-point solutions corresponds to de-Sitter expansion. The others are either unstable or saddle nodes. Numerical integration of the dynamical system are performed and plotted confronting with $H(z)$ data. It is found that for flat universe, $H(z)$ observational data favors large negative value of NMDC coupling, $\kappa$. Larger holographic contribution, $c$, and larger negative NMDC coupling increase slope and magnitude of the $w_{\text{eff}}$ and $H(z)$. Negative $\kappa$, can contribute to phantom equation of state, $w_{\text{eff}} < -1$. The NMDC-spatial curvature coupling could also have phantom energy contribution. Free negative spatial curvature term can also contribute to phantom equation of state, but only with significantly large negative value of the spatial curvature. As one possible solution to the Hubble tension is phantom equation of state. The model could give phantom equation of state for $\kappa = -200$ and high value of $c$ for both flat and open cases.
Comment: 15 pages, 4 figures